Do ontologically diverse functional T cell subsets (suppressor and helper) share the same basic structural mechanisms for antigen recognition? Hybridoma antibodies with specificity for T cell antigens mapping to the region coding for Tsd (a suppressor cell constant region receptor determinant) on chromosome 12 in the mouse will be used to construct a surface topological map of T cell receptors with respect to Ia, light chain and Ly antigens. The major questions to be asked are whether T suppressor cell antigen receptors and T helper cell receptors are structurally very similar or rather share only VH gene products and no light chain, constant region, or I-A products. It is predicted that Tsd is only the first in a series of T cell products which will map to this region, which may code for the production of a panel of cell constant region gene products, characteristic of diverse T cell subsets. This grant seeks support to produce and screen for a panel of hybridoma antibodies with specificity for different functional subsets. BALB/c (Igh-1a H-2d) animals will be immunized with C.AL-20 (Igh-1a H-2d) selected T cells and immune spleen cells fused with a BALB/c nonsecreting myeloma, P3.U., NS-1, or SP-2 Ag-14. Anti-sera will be screened in a radioimmunoassay on Con A activated C.AL-20 and BALB/c monolayers. Positive antibodies will be characterized functionally and used in a competitive radioimmunoassay to access the steric relationship to known T cell surface antigens.